EUV Mirror Surface Profile Correction via Selective Layer Shaving
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Solution Overview
Problem
In EUV lithography systems, multilayer-film reflective mirrors with precise surface profiles are difficult to manufacture due to the challenge of maintaining accurate reflectance and phase integrity after layer shaving, as conventional capping layers like ruthenium cause irregularities in light propagation.
Innovation Solution
A method involving a multilayer film with alternating Mo and Si layers, where localized layer removal is followed by deposition of a Si single-layer film to restore the surface profile, and a uniform capping layer is applied to prevent phase and reflectance changes, ensuring precise surface profiles and minimizing aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ru capping layer is applied over the entire surface including shaved regions, then oxidation and carbon contamination of the Mo layer are prevented, but the phase of the reflected wavefront changes considerably and reflectance becomes irregular
Solution Approach 1:
The patent applies the Ru capping layer selectively only in regions where Mo layers have been shaved away, rather than uniformly across the entire surface. This localized application prevents oxidation and contamination of exposed Mo surfaces while avoiding the phase and reflectance irregularities that would result from depositing Ru over the complete mirror surface, thereby resolving the contradiction between protection and optical precision
2Manufacturing precision
If layer shaving is performed to correct surface figure errors, then aberrations from sub-nanometer figure errors are corrected, but the Mo layer becomes exposed to atmosphere causing oxidation
Solution Approach 1:
The patent performs layer shaving to correct surface figure errors, and then immediately applies a Ru capping layer in the shaved regions to prevent oxidation of the exposed Mo layer. This preliminary protective action counteracts the harmful effect of oxidation that would otherwise occur after the necessary surface correction, resolving the contradiction between achieving precision through shaving and maintaining reliability against environmental degradation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the creation of multilayer-film reflective mirrors with highly precise surface profiles, maintaining accurate reflectance and phase characteristics, thereby enabling satisfactory exposure of fine pattern features in EUV lithography systems.
Implementation Method 1
multilayer-film mirrors in which the respective phases of multiple fronts of weakly reflected light at layer interfaces are superposed constructively in the reflected light to obtain high overall reflectance
Implementation Method 2
a single-layer film of Si, or of a material comprising Si, is situated on the top surface of the multilayer film to fill regions of the multilayer film from which material has been removed
Implementation Method 3
a single layer of Si or other oxidation-preventing substance, a ruthenium (Ru) layer, or other 'capping' layer (to prevent oxidation of the exposed Mo layer) is normally applied at least in the shaved regions
Data Source
AI summary
Multilayer-film (MLF) reflective mirrors are disclosed that have a highly precise surface profile. An exemplary MLF reflective mirror includes multilayer film in which layers of molybdenum (Mo) and layers of silicon (Si) are periodically deposited in an alternating manner on the surface of a mirror substrate. One or more selected regions of the multilayer film have been “shaved” away layer-wise as required to impart an in-plane distribution of removed material sufficient to correct a wavefront error in light reflected from the mirror. After such “layer-machining,” a single-layer film of Si (or Si-containing material) is applied to fill in the machined areas and restore the original contour, as designed, for the surface of the multilayer film. I.e., the Si film has a thickness distribution corresponding to the depth profile of material removed from the multilayer film. A capping layer can be deposited uniformly on the surface of the single-layer film.